The invention relates to a decoupler that represents a device formed as a torque-transmission system between a shaft and a belt pulley of a starter generator, wherein the belt pulley can rotate relative to the shaft. For reducing rotary oscillations between the belt pulley and the shaft, the decoupler comprises a damping device including at least one spring element.
For internal combustion engines used in motor vehicles, two separate assemblies are conventionally used for generating power and for starting the internal combustion engine, a starter motor (also called a cranking motor) and a generator. The starter motor is used exclusively for starting the internal combustion engine and the generator is used for operating all of the electrical loads in the internal combustion engine and the motor vehicle.
In belt-driven starter generators (RSG systems), in the start cycle, the generator belt pulley transmits the torque for starting the internal combustion engine. Immediately after a successful start of the internal combustion engine, the starter generator is driven by the internal combustion engine, wherein, independent of the operating cycle of the starter generator, the direction of rotation of the traction mechanism drive is unchanged. Due to the rotational irregularity of the internal combustion engine, the starter generator requires a so-called generator decoupling device that is realized by a decoupler that can start and stop and that has rigid end stops by which, in the start cycle, the starting moment can be introduced into the belt drive. It has proven to be problematic that at the beginning of the start process or while running through the natural resonance rotational speed of the decoupler, the rotation of the generator shaft relative to the generator belt pulley is very large and thus the end stop is reached, whereby a pulse is introduced into the belt drive. This pulse generates disadvantageous force spikes that are transmitted to assemblies arranged adjacent to the starter generator.
It is known to equip motor vehicles with a so-called start-stop function in which the internal combustion engine is automatically turned off after a fixed time interval in the idling cycle and is automatically started after the gas pedal is actuated. For this function, a starter generator according to WO 2007/121582 A1 is suitable.
From DE 10 2006 057 793 A1 a belt-driven starter generator is known to which a free-running belt pulley that is also designated as a decoupler belt pulley is allocated. This belt pulley can rotate relative to a shaft of the assembly via a bearing. For transmitting the rotational movement of the belt drive from the belt pulley to the shaft and in order to simultaneously equalize the rotational irregularity introduced into the belt drive in the internal combustion engine, a spring element is inserted between the belt pulley and the shaft. Accordingly, in this way, the effective torsional rigidity of the spring element allows relative rotation between the belt pulley and the shaft.